xe2x80x9cThis application claims priority to Taiwan patent application Ser. No. 088121714, filed Dec. 10, 1999.xe2x80x9d
The present invention relates to a method for preparing a barium fluorotitanate (BaTiF6) powder and barium titanate (BaTiO3), and more particularly to a method for growing a barium titanate thin film on a silicon wafer from the barium fluorotitanate powder at a low temperature.
Because of its high dielectric constant, barium titanate (BaTiO3) is widely used in alternative charge storage insulators of semiconductor devices, for example, dynamic random access memories (DRAMs) or micro-electromechanic systems (MEMS). In addition, barium titanate can be used to replace silicon dioxide (SiO2) as a gate oxide of metaoxide-silicon field-effect transistor (MOSFET) in the process for manufacturing semiconductors.
The methods for preparing barium titanate are generally divided into two types. One is a dry growing method such as chemical vapor deposition, metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and sputtering. The apparatuses for performing this method are very expensive, and the high working temperature will induce thermal stress to the apparatuses and degenerate the gate oxide. The other is a wet growing method such as sol-gel process and liquid phase deposition (LPD). However, a sintering process at high temperature from about 600xc2x0 C. to 1000xc2x0 C. is necessary to prepare barium titanate by the sol-gel method. Thus, the defects resulted from the high temperature process could not be avoided.
In order to solve the above problems, the present invention provides a method for growing a barium titanate thin film at a low temperature and stabilizing the materials. In addition, the present invention also provides a method for increasing the precision of the process effectively.
It is therefore an object of the present invention to provide a method for preparing a barium fluorotitanate (BaTiF6) powder.
In accordance with the present invention, the method for preparing the barium fluorotitanate (BaTiF6) powder includes steps of a) mixing a hexafluorotitanic acid (H2TiF6) solution and a barium nitrate (Ba(NO3)2) solution at a specific temperature to produce the barium fluorotitanate precipitate and b) isolating and drying the barium fluorotitanate precipitate powder.
Preferably, the specific temperature is in the range of 0xc2x0 C. to 100xc2x0 C.
Preferably, the concentration of the hexafluorotitanic acid solution is in the range of 0.01 M to 6.10 M. The concentration of the barium nitrate solution is in the range of 0.01 M to 0.30 M.
The volume ratio of the hexafluorotitanic acid solution to the barium nitrate solution is any value but preferably between 10:1 and 10:6.
More specially, the barium fluorotitanate is iosolated by heating.
It is another object of the present invention to provide a method for growing a barium titanate (BaTiO3) thin film on a silicon wafer.
In accordance with the present invention, the method for growing the barium titanate thin film on the silicon wafer includes steps of a) dissolving a barium fluorotitanate powder in water to form a barium fluorotitanate solution, b) introducing a boric acid (H3BO3) solution to the barium fluorotitanate solution to form a mixture, and c) immersing a silicon wafer to the mixture at a specific temperature to grow a barium titanate thin film on the silicon wafer.
Preferably, the specific temperature is in the range of 0xc2x0 C. to 100xc2x0 C.
Preferably, the concentration of the barium fluorotitanate solution is in the range of 0.01 M to 0.06 M. The concentration of the boric acid solution is in the range of 0.01 M to 0.95 M.
Preferrably, the water used in the step (a) is deionized water.
Certainly, the barium titanate thin film can be deposited on the customarily used silicon substrate or other substrates.
It is still an object of the present invention to provide a method for growing a barium titanate thin film on a silicon wafer.
The method for growing a barium titanate thin film on a silicon wafer includes steps of a) mixing a hexafluorotitanic acid (H2TiF6) solution and a barium nitrate (Ba(NO3)2) solution at a specific temperature to produce a barium fluorotitanate (BaTiF6) powder, b) dissolving the barium fluorotitanate powder in water and introducing a boric acid (H3BO3) solution to form a mixture and c) immersing a silicon wafer to the mixture at a specific temperature to grow a barium titanate thin film on the silicon wafer.
Preferably, the specific temperature is in the range of 0xc2x0 C. to 100xc2x0 C.
Preferably, the concentration of the hexafluorotitanic acid solution is in the range of 0.01 M to 6.10 M.
In accordance with another aspect of the present invention, the concentration of the barium nitrate solution is in the range of 0.01 M to 0.30 M.
Preferably, the volume ratio of the hexafluorotitanic acid solution to the barium nitrate solution is preferably between 10:1 and 10:6.
Preferably, the concentration of the boric acid solution is in the range of 0.01 M to 0.95 M.
Certainly, the barium titanate can also be deposited on any other materials as on silicon.